Introduction & Objectives

Determining cause of death when cetaceans strand is needed to dispel misinformation and ensure accurate public understanding of stranding cause. This is especially relevant in areas that are critical to Navy training and testing operations such as the Mariana and Hawaiian Islands. Prior work of the Health and Stranding Lab has demonstrated that infectious disease poses a significant threat to Pacific Island cetaceans (whales, dolphins and porpoises), with natural disease accounting for 62% of stranded cetaceans that were examined with significant pathology. 

Technical Approach

Studying infectious diseases involves both direct and indirect measures of the presence of pathogens and their impact. Direct and indirect methods of investigating disease are complementary, improving understanding of the factors that contribute to animal mortality. Direct methods often rely on detection of the pathogen of interest itself by using procedures that directly stain the pathogen in infected tissues, grow the pathogen from tissue cultures, or amplify the minute amounts of genetic material of the disease present in infected tissues through conventional and quantitative PCR. Indirect methods of disease research rely on detection of an animal's response to an infection. This includes serology, which allows for indirect study of diseases by testing for the presence of disease specific antibodies in the bloodstream that are generated in response to exposure to the pathogen of interest. Specific indirect testing methodologies include agglutination tests, immunofluorescent response, Western blot, and enzyme-linked immunosorbent assays (ELISA).

Progress & Results

This project includes initial efforts to validate use of a commercial enzyme immunoassay intended for the agricultural morbillivirus peste des petits ruminants (PPR) tested for use with cetaceans. A suite of tissue samples and fluids collected from a Fraser’s dolphin (Lagenodelphis hosei) and a Longman’s beaked whale (Indopacetus pacificus), each previously confirmed to have differing strains of CeMV with severe infection, were tested with the PPR enzyme immunoassay. Antibodies were detected in all tissues and fluids tested for the Fraser’s dolphin with the exception of urine and in two of four tissues tested in the Longman’s beaked whale. Further testing included serum samples collected from 27 stranded cetaceans that represented ten species with unknown infection status. Ten individuals were seropositive for CeMV antibodies, indicating a 37% exposure rate.

Toxoplasmosis represents a significant disease threat to Hawaiian marine mammals, with fatally disseminated cases documented in monk seals, three spinner dolphins and a bottlenose dolphin. Cetacean carcass recovery rates in the Hawaiian Islands are extremely low, averaging near 1% (West and Baird, unpublished data). Prior spinner dolphin deaths were likely underestimated in projections of 60 dolphin deaths based on three cases of fatally disseminated toxoplasmosis (Landrau-Giovanetti et al. 2022). An evaluation of cetacean exposure to the Toxoplasma gondii parasite has not previously been conducted in the central Pacific. This study included serological diagnosis of T. gondii from previously stranded cetaceans to investigate pathogen exposure rate. Serum samples collected from 35 individuals that represent 12 different cetacean species were tested via enzyme immunoassay for the presence of T. gondii antibodies. Three individuals tested positive (seropositivity rate of 8.6%). 

Matching meat juice samples were also tested for T. gondii antibody presence in the 35 individuals where serum samples were available and we found consistent results in the meat juice sample matrix. Meat juice samples from a range of tissue types were tested for an additional 159 individual animals where serum was unavailable. Sixteen additional animals were positive in at least one meat juice tissue type, with an overall meat juice exposure rate of 9.7% in individuals tested across multiple species of Hawaiian cetaceans.